I use Jekyll[1]. It's quite popular which implies that it's easy to search for answers online or find steps to some specific customization you might need.
Same, although I recommend not relying on GitHub pages for generating the site due to the age of the gems available on it. I've initially kept my blog compatible with it even though I'm serving it from my NAS, but I ended up ditching compatibility because of that in order to use more modern versions.
[1] https://blog.quipu-strands.com/jensens_inequality